Optical networks are becoming widely used for distributing both high and low speed data over varying distances. Typically, an optical network is comprised of a number of network elements (NE) that are connected to each other in a variety of configurations so as to form a unified communication network. The communication network may extend over a small area, such as a company wide network, or may cover large distances, such as in regional or nationwide networks. Typically, the NE's allow network clients to input data for transmission over the network and to receive data transmitted over the network from other locations. Thus, data may be added or dropped from the network at NE locations as the data flows from point to point throughout the network.
Typically, a network element includes one or more wavelength converters that convert optical signals from one wavelength to another. The wavelength converters are used as part of input or output tributaries associated with a network element. For example, an input tributary allows a network user to input signals at an NE for transmission over the network, and an output tributary allows a network user to receive signals at an NE that have been received from the network.
FIG. 1 shows a typical network element 100 that receives signals transmitted over a communication network and includes an output tributary that produces an output signal to a local user. The network element couples to the communication network as shown at 102. The input signal from the network may be received by a line receiver 104. The output of the line receiver 104 is coupled to a demulitplexer stage 106 that filters the received input signal to produce a demultiplexed signal 108 that is intended to be input to a transceiver circuit 110. The transceiver circuit may convert the received signal 108 to a different optical wavelength or an electrical signal for output as output signal 112.
It is very important to control the optical power input to the transceiver circuit 110 so that the transceiver operates optimally. If the power is too high, then the transceiver hardware can be damaged, and/or errors may creep into the signals. If the power is too low, then again, the signals may not remain error-free. The network designer calculates the optimal receive power range for the transceiver input and the network installer (technician) needs to ensure that the optical received power at the transceiver is indeed in that range. For some traffic types, the optimal range is extremely narrow, and so an accurate transceiver input power setting is required.
Usually, the network is designed such that the received power is never too low. In many cases, the design ensures that the power received at the transceiver is very high. In this case, typical systems use a “pad” or a fixed attenuator 114 just before the transceiver circuit to control the power level seen at the input of the transceiver. The attenuator 114 operates to reduce the power level of the signal input to the transceiver by a fixed amount.
However, the process of installing pads is a labor-intensive procedure that involves the physical presence of personnel at each site. The value of the pads may have to change during network upgrades, even if the upgrades occur at a different site in the optical network. There may be dozens of pads that need to be adjusted. During a network switching event, power changes to the signal 108 may occur, with the result that the pad value may not be accurate enough or may require additional adjustment to obtained the desired power level at the transceiver 110 input. Furthermore, the problems associated with input power levels variations exist for many other components in a network element, not just to transceiver circuits.
Therefore, it would be desirable to have a way to optimize received power at an optical receiver (or other component) in a network element without having to install pads that are labor intensive to maintain and may not provide the accuracy required.